The Collaborative International Dictionary of English v.0.48:

Semipermanent \Sem`i*per"ma*nent\, n.
   Half or partly permanent.
   [1913 Webster]

WordNet (r) 3.0 (2006):

semipermanent
    adj 1: relating to or extending over a relatively long time;
           "the long-run significance of the elections"; "the long-
           term reconstruction of countries damaged by the war"; "a
           long-term investment" [syn: long-run, long-term,
           semipermanent]