Gnomish
beltha-
verb. to open out (transitive), expand, unroll, set sail
Beware, older languages below! The languages below were invented during Tolkien's earlier period and should be used with caution. Remember to never, ever mix words from different languages!
A verb appearing as G. beltha- “open out (transitive), expand, unroll, set sails” in the Gnomish Lexicon of the 1910s (GL/22), clearly based on the early root ᴱ√VELU (or ✱ᴱ√BELU) “unroll” (QL/100). The verb G. beltha- was first translated as “to swell, belly (of sails), open out, expand (intransitive)”, but this intransitive sense was transfered to G. belu-.
Neo-Sindarin: Since I retain the Neo-Root ᴺ√BELU “unroll, ✱unfurl”, I would retain ᴺS. beltha- “to open out, expand, unroll, set sail”, properly pronounced bella- with Welsh-like long voiceless ll. I would also use this verb intransitively to mean “to swell, belly (of sails)”, mostly because we don’t know how u-verbs are conjugated in Sindarin.