ADJECTIVE (2)

1. often improvised or impromptu;
- Example: "an ad hoc committee meeting"

2. for or concerned with one specific purpose;
- Example: "a coordinated policy instead of ad hoc decisions"


ADVERB (1)

1. for one specific case;
- Example: "they were appointed ad hoc"

WordNet (r) 3.0 (2006):

ad hoc
    adv 1: for one specific case; "they were appointed ad hoc"
    adj 1: often improvised or impromptu; "an ad hoc committee
           meeting"
    2: for or concerned with one specific purpose; "a coordinated
       policy instead of ad hoc decisions"