Having been silent for a long time, I am back with a posting on time – an enduringly fascinating question. The Celtic words for “time” are OIr. aimser, W amser, OCorn. anser [sic], OBret. amser, ModBret. amzer. These words can also be used to refer to the “weather”. These terms are evidently related to OIr. amm (o?, n) “time”, derived from its preform via the addition of a suffix *-e/i(n)stero/ā. Gaul. amman (Calendar of Coligny), which looks like a neuter n-stem, is also believed to be related, although it cannot be an exact equation with OIr. amm due to the different stem formation. The further etymology of amm and aimser is usually regarded as unclear (LEIA, EDPC), although it has been suggested to connect it with Hitt. hamesha- “Spring”, deriving both from a root *√h2em-, which, however, is not attested anywhere else. Obscurum per obscurius.
I want to suggest to derive it from the PIE root *√h2et- “to go” which underlies the words for “year < *one cycle/course/perambulation of the sun” in Lat. annus, Osc. akeneí, Umbr. acnu, Goth. aþn* and ataþn* < *h2et-no-. Two reconstructions are conceivable, both meaning approximatively “the going/course (of time)”:
1. *h2et-mo- > *atmo- > PC *ammo-: In order for this etymology to work, it has to be assumed that *-tm- resulted in *-mm- in Celtic. I cannot think of a counter-example, but would be grateful for any suggestion. *-dm- behaves differently, depending on position or morphological transperancy of the word. In OIr. ammus “attempt” < *ad-med-tu- it has evidently been assimilated to *-mm-, but OIr. naidm “binding” < *nad-man- and feidm “effort, work” < *u̯ed-man- shows the retention of the cluster, perhaps under influence from paradigmatically related verbal forms.
2. Phonologically neater is *h2et-s-mo- which undoubtedly leads to the expected result, via *atsmo- > *asmo- > *ammo-. In this solution, *-smo- could either be the “sigmatic” variant of *-mo-, or *-mo- has been added to an s-stem *h2etes-, for which, however, there is no other evidence.
If this etymology is correct, it would imply a cyclical concept of time.