borderline

Short definition from Wiktionary

Adjective

1. 1
   Nearly; not clearly on one side or the other of a border or boundary, ambiguous.
2. 2
   Of questionable taste or acceptability; approaching bad taste.
3. 3
   Exhibiting borderline personality disorder.

Adverb

1. 1
   Nearly; not entirely but nevertheless to a great extent.

Noun

1. 1
   A boundary or accepted division; a border.
2. 2
   Ellipsis of borderline personality disorder.
3. 3
   A person who has borderline personality disorder.

Verb

1. 1
   To border, or border on; to be physically close or conceptually akin to.