1. Not able to be counted (e.g. because too many to count) 
2. (grammar) of a word that does not have a plural form

Encyclopedia: Uncountable

• half-mast
• half-moon
• half-pay
• half-pint
• half-price
• half-relief
• half-seas-over
• half-size
• half-slip
• half-staff
• half-term
• half-timber
• half-timbered
• half-tracked
• half-truth
• half-wit
• half-witted
• half-yearly
• halfback
• halfbeak
• halfhearted
• halfpenny
• halfpennyworth
• halftime
• halftone