投機

to speculate (on financial markets) / opportunistic / congenial / agreeable

to cast / to send / to throw oneself (into the river etc) / to seek refuge / to place oneself into the hands of

(bound form) machine; mechanism / (bound form) aircraft / (bound form) an opportunity / (bound form) crucial point; pivot / (bound form) quick-witted; flexible / (bound form) organic

to seize every opportunity / to be full of tricks

speculator

the conversation is disagreeable (idiom)

when views are irreconcilable, it's a waste of breath to continue discussion (idiom)

buying and selling on speculation

speculation and profiteering (idiom); buying and selling on speculation