The morpheme য়া occurs in many words, such as
য়া-হীপ্পা (with a slight sound change, য়াইহীপ্পা as in য়াইহীপ তানবা)
য়া-তাবা (and its derivative য়া-তাফম).
To this, we can add the slightly complicated idiom য়াম্ফক তাবা (yamfak taba), though it needs another separate article to deal with the additional and changed sound /m/ in it.
Hyphen has been inserted in the above words to mark য়া off the rest of the words.
I have yet to work out the definite meaning of this morpheme but, at the moment, it seems that য়া means “body.” If this is right, then য়াহৌবা (য়া = body; হৌবা = to get up, begin, start) would mean (of the body) to get up, start, begin and set to work. The body rests the long hours of night, and when morning comes, the body is up (হৌবা) from sleep, and you (or your body) begins (হৌবা) the day–you get out and set to (হৌবা) work. Your body gets up, sets out, set to work, and work all day. The time you (or your body, য়া) wakes up and get up (হৌবা) is the morning. You do য়াহৌবা (wake up, get up) in the morning.
In the evening, when the sun sets, you (the body, য়া) come back from the day’s work and enter or get into (চঙবা) your house. The time of the day when you come back from work and get back home (and enter into your house) is য়া-চঙবা (which is, sunset, evening, nightfall).
Though য়াচঙবা and য়াহৌবা are used to mark two specific times of the day–morning and sunset, respectively–the morpheme য়া has nothing to do with নুমীৎ, the sun, which universally has to do with time-marking words across all languages. One easy proof is that Manipuri has নুমীৎ য়াচঙবা and (নুমীৎ) য়ূমচঙবা to mean sunset. নুমীৎ য়াচঙবা literally means the sun (or its body) getting back into its house; however, it is worth assuming that য়াচঙবা must have already lost the original sense of the body getting back into the house with only the sense of the time of the end of the day (or sunset) remaining. য়ূমচঙবা is metaphorical and the symbolism is readily in it, without any attempt at literalness.
য়াকৈবা is a phonological variant of য়াকায়বা, which means (of the body) to break up or out (কায়বা, থোকপা) from sleep or night or what (such as the state) it was in while asleep. য়াকৈবা is considered more literary and is found in many ancient literary texts and pena songs; for example, য়াকায়রোল sung in the accompaniment of the pena to wake up the deity at dawn during lai haraoba.
য়াচেপ্পা is for your body to lie on one side–you (or you body, য়া) lie on your side (চেপ্পা). When you sleep, you most of the time lie on your side (চেপ্পা), and thus, in time, the word চেপ্পা comes to acquire a new meaning–to go to be or lie or sleep. চেপ্পা in the newer (which is very old now) is considered more dignified.
When you sleep, you don’t just fall flat like dead or a log. You turn or your body (য়া) turns (ওনবা) and change the side of lying. You do য়াওনবা.
When you য়াওনবা while asleep, the side of your body you sleep on change, and it relaxes your muscles. When a society has lived in one particular situation or structure or system for a long time, many people in this society becomes dissatisfied with the status quo. They want a change–the body of the society to turn or go for a change. Such a change is called য়াওল. য়াওল is a metaphorical derivative of য়াওনবা. য়াওল্লোই is another derivative, formed with the suffix -লোই (doer, agent, professional) added to য়াওল.
You usually sleep at a particular place–in your house. Or rather a particular place in your house. If you go to another place outside your house, and sleep at a place you don’t usually sleep at, you (or your body য়া) spend the night (লেকপা) there. You do য়ারেকপা. It may be under a tree, in the hay stack, or at your neighbor’s or at your friends or relatives. If you spend one night or two or so at a place that is not where you usually live, you do য়ারেকপা there–your body (য়া) spends (লেকপা) the unusual night(s) there.
When you have a deep, sound sleep, your body (য়া) falls (তাবা) motionless like a lifeless object. If you sleep like this, you do য়াতাবা. য়াতাবা is rather literary and has derived meanings.
Some other interesting occurrences of য়াক in which we have yet to work out the meaning are য়াখোয় or য়াকখোয়, য়াক (অয়াক, ঐয়াক) and their possessive, nominative (marked and unmarked) and objective derivatives. I think “body” as the meaning of য়া (য়াক in these words) works here as well. It is probable that য়া is shortened from য়াক, and the semi-vowel /j/ often changes to /h/ in the singular. This /h/ can turn to /kʰ/ as in তোম্বখোয়দি, মীখোয়দি, ঐখোয়দি (=ঐদি), etc.