Occasional

• (a.) Produced by accident; as, the occasional origin of a thing. • (a.) Of or pertaining to an occasion or to occasions; occuring at times, but not constant, regular, or systematic; made or happening as opportunity requires or admits; casual; incidental; as, occasional remarks, or efforts.
Found on http://thinkexist.com/dictionary/meaning/occasional/

Occasional

Oc·ca'sion·al adjective [ Confer F. occasionnel .] 1. Of or pertaining to an occasion or to occasions; occuring at times, but not constant, regular, or systematic; made or happening as opportunity requires or admits; casual; incidental; as, occasional remarks, or efforts. «...
Found on http://www.encyclo.co.uk/webster/O/7

occasional

a poem written to describe or comment on a particular event or occasion. Examples are Andrew Marvell's 'Horatian Ode' and Alfred lord Tennyson's 'The Charge of the Light Brigade.'
Found on http://rpo.library.utoronto.ca/display_rpo/terminology.cfm#acatalectic

occasional

appearing or occurring irregularly and according to no fixed or certain scheme.
Found on http://users.ugent.be/~rvdstich/eugloss/DIC/dictio60.html

occasional

Appearing or occurring irregularly and according to no fixed or certain scheme. ... (18 Nov 1997) ...
Found on http://www.encyclo.co.uk/local/20973
No exact match found