Gnomish
reth-
verb. to save, rescue, preserve
gretha-
verb. to save, rescue, preserve
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 gretha- “save, rescue, preserve” in the Gnomish Lexicon of the 1910s (GL/42), clearly based on the early root ᴱ√RESE [REÞE] (QL/79; GL/65). Elsewhere in the Gnomish Lexicon Tolkien had reth- “save, rescue, preserve”, but this variant was deleted (GL/65).
Neo-Sindarin: For purposes of Neo-Sindarin, I would updates these verbs to Fiona Jallings’s neologism ᴺS. reitha- “to rescue, save (from ruin, peril, loss)”, inspired by Q. rehta- of the same basic meaning.