Géb-sa lethrand dús in ba cubaid frissa ngéba-som.
'Géb' and 'géba' are future forms of 'gaibid'. The basic meaning is
"take", but it's one of those verbs that actually has a multitude of
'-sa' is the first person singular and '-som' the third person singular
'lethrand' is a compound of 'leth' - "half" and 'rann' - "quatrain".
'dús in' - "whether', introduces a dependent question after verbs of
asking, seeing, etc. Here it refers back to 'atˇchicera' in the
'cubaid - "fitting, meet", DIL,C,578,58 cites our line and gives a
translation of "to see if it fits yours (half quatrain)".
'frissa' looks like the preposition frith + the relative particle.
Because of the nasalization, if I understand GOI #497, this particle
must be 'a' - "while, when" rather than 'a' - "that, which'.
So a literal translation might be:
"I will do a couplet (you will see) whether it will be fitting against
when he will do."