The form lhegin in the published Etymologies might be a misreading for lhegrin, see VT/45:25. As noted by Bertrand Bellet, the two forms are listed side by side, and they may simply be doublets, but it is also possible that we have here a singular followed by its plural.
celegadjective. *hasty, *[N.] agile, *swift
celegadjective. swift, agile, hasty
lagoradjective. swift, rapid
adj. swift. Noro lim, noro lim Asfaloth. 'Run swift, run swift Asfaloth'. Q. limbe,#linta.
1) celeg (agile), lenited geleg, pl. celig, 2) lagor, analogical pl. legyr, 3) legrin (rapid), no distinct pl. form, 4) lint (no distinct pl. form)
celeg (swift), lenited geleg, pl. celig
heledh (i cheledh, o cheledh), pl. helidh (i chelidh) if there is a pl.
* lagoradjective. swift, rapid
* brilnoun. glass, crystal