1) Addon 2) Eke 3) Elongate 4) Extend 5) Prolong 6) Protract 7) Rehem 1) Become long or longer 2) Draw out 3) Extend 4) Exclusively Anglo word 5) Exclusively Saxon word 6) Get longer 7) Increase 8) Make longer 9) Prolong 10) Stretch 11) Stretch out 12) To become longer 13) Word of purely Anglo origin 14) Word with Anglo-Saxon origins 
• (v. t.) To extent in length; to make longer in extent or duration; as, to lengthen a line or a road; to lengthen life; -- sometimes followed by out. • (v. i.) To become longer.
The opposite of 'Shorten'. Referred to odds getting longer, that is, more attractive to the bettor.
Length'en (-'n) transitive verb [ imperfect & past participle Lengthened (-'nd); present participle & verbal noun Lengthening (-'n*ĭng).] To extent in length; to make longer in extent or duration; as, to lengthen a line or a ...Length'en intransitive verb To become longer. Locke. 
[v] - make longer 2. [v] - become long or longer
verb become long or longer; `In Spring, the days lengthen`
Odds lengthen when they go up - for example, from 3-1 to 4-1. This is also known as "drifting".
alargar