tic-tac 
(also tick-tack)
noun [mass noun]
(In the UK) a kind of manual semaphore used by racecourse bookmakers to exchange information.
Origin
Mid 16th century (denoting a repeated ticking sound): imitative; compare with tick-tock. The current usage (originally slang) dates from the late 19th century.
- chemosmosis
- chemosmotic
- chemosphere
- chemostat
- chemo-statical
- chemosterilant
- chemosurgery
- chemosynthesis
- chemosynthetic
- chemosynthetically
- chemotactic
- chemotactical
- chemotactically
- chemotactism
- chemotax
- chemotaxic
- chemotaxis
- chemotaxonomic
- chemotaxonomical
- chemotaxonomically
- chemotaxonomist
- chemotaxonomy
- chemotherapeutic
- chemotherapeutics
- chemotherapist