溯る[sakanoboru] to go back
溯及[sokyuu] tracing back
溯源[sogen] returning to the origin

溯航[sokou] going upstream
溯河魚[sakkagyo] anadromous fish (fish that migrates upstream, e.g. salmon)

運航[unkou] operating (e.g. ships, aircraft)
えい航[eikou] towing (a ship)
英国航空[eikokukoukuu] British Airways
往航[oukou] outward voyage
廻航[kaikou] navigation

寄航[kikou] stopping at a port
休航[kyuukou] suspension of sailings
近接航空支援[kinsetsukoukuushien] close air support
欠航[kekkou] flight cancellation
航宇[kouu] aerospace

行けない[ikenai] wrong
行る[yaru] to send
オリエント急行[orientokyuukou] Orient express
カ行[kagyou] classification for Japanese verb with the dictionary form ending in "ku"
ガ行[gagyou] classification for Japanese verb with the dictionary form ending in "gu"

サ行[sagyou] classification for Japanese verb with the dictionary form ending in "su"
ザ行[zagyou] classification for Japanese verb with the dictionary form ending in "zu"
スパイ行為[supaikoui] espionage
タ行[tagyou] classification for Japanese verb with the dictionary form ending in "tsu"
ダ行[dagyou] classification for Japanese verb with the dictionary form ending in "dzu"

遡る[sakanoboru] to go back
遡及[sakkyuu] tracing back
遡源[sakugen] returning to the origin
遡及的[sokyuuteki] retroactive
遡上[sojou] going upstream

遡航[sokou] going upstream
遡求[sokyuu] redemption
遡河魚[sokagyo] anadromous fish (fish that migrates upstream, e.g. salmon)
遡及書誌[sokyuushoshi] retrospective bibliography
遡求権[sokyuuken] right of recourse