off chance
noun informal uk/ˈɒf ˌtʃɑːns/ us/ˈɑːf ˌtʃæns/
on the off chance 抱着一线希望;侥幸一试，碰运气
hoping that something may be possible, although it is not likely
I applied for the job on the off chance that they might like me, but I didn't seriously expect to get it. 我怀着一线希望申请了这份工作，不过我没真的指望能得到它。