Definition of sissies:
(n) :
(sometimes derogatory, colloquial) An effeminate boy or man.
(n) :
(sometimes derogatory, colloquial) A timid, unassertive or cowardly person.
(adj) :
(derogatory) Effeminate.
(adj) :
(derogatory) Cowardly.
(n) :
(BDSM) A male crossdresser who adopts feminine behaviours.
(n) :
(dated, colloquial) Sister; often used as a term of address