transitive verb

1. to join (one thing to another); attach; connect
2. to make fast or secure, as by locking, shutting, buttoning, etc.; fix firmly in place
3. to hold, fix, or direct (the attention, gaze, etc.) steadily on something
4. to cause to be connected or attributed; impute to fasten a crime on someone
5. to force (oneself) on or upon another in an annoying way

Etymology: ME fastnen < OE fæstnian < base of fæst: see fast

intransitive verb

1. to become attached or joined
2. to take a firm hold (on or upon); seize; cling
3. to concentrate (on or upon)