Wordnet 3.0
NOUN (1)
1. 
 a material that softens when heated and hardens again when cooled; 
[syn: thermoplastic, thermoplastic resin]
ADJECTIVE (1)
1.  having the property of softening or fusing when heated and of hardening and becoming rigid again when cooled; 
- Example: "thermoplastic materials can be remelted and cooled time after time without undergoing any appreciable chemical change"
WordNet (r) 3.0 (2006):
thermoplastic
    adj 1: having the property of softening or fusing when heated
           and of hardening and becoming rigid again when cooled;
           "thermoplastic materials can be remelted and cooled time
           after time without undergoing any appreciable chemical
           change" [ant: thermoset, thermosetting]
    n 1: a material that softens when heated and hardens again when
         cooled [syn: thermoplastic, thermoplastic resin]