The slash sign in minlamad thent/estent might indicate either variant forms of an adjective, or a sequence of two short verse units, possibly of alliterating half-lines, see Tolkien's Legendarium p. 122
Sindarin
esten
adjective. thenna
estent
adjective. (very?) short
esten(t)
adjective. short
estent
thenta
Q. thenta, senta.
thenn
thenna
adj. Q. thenna, senna. >> esten
thent
short
thent (pl. thint), also ?estent (pl. estint).
thent
short
(pl. thint), also ?estent (pl. estint).
then
adjective. short
thenn
adjective. short
thent
adjective. short
thent
adjective. short
thent
thenta
Q. thenta, senta.
nuitha
stop short
(i nuitha, in nuithar) (prevent from coming to completion; stunt; not allow to continue) (WJ:413)
thinnas
shortness
(also used for a “breve”, a mark indicating that a vowel is short). Verb
adj. Q. thenna, senna. >> thenn