Has multi definitions
1) -military- Mobile Army Surgical Hospital. Also TV show of same name.
2) -drugs- To smoke yourself into a state of near unconciousness
3) -UK Slang- Mashed potato's
4) -Urban street slang- To destroy, mangle, wreck.
1) He served in a mash unit in Korea
2) Tonight I'm gonna get mashed
3) 'Give us a bash at the bangers
and mash like me mother used to make' (old music hall song)
4) He dissed me so I mash him up bad.