[1] : WordNet (r) 2.0

clock in
     v : register one's arrival at work syn: punch in, clock on
         ant: clock out, clock out
see also:
punch in clock on clock out 

[2] : Moby Thesaurus II by Grady Ward, 1.0

37 moby thesaurus words for "clock in":
   accomplish, achieve, approach, arrive, arrive at, arrive in,
   attain, attain to, be received, blow in, bob up, check in, come,
   come in, come to, come to hand, fetch, fetch up at, find, gain,
   get in, get there, get to, hit, hit town, make, make it, pop up,
   pull in, punch in, reach, ring in, roll in, show up, sign in,
   time in, turn up

Clock >> C Words
Clock, definition of term: Clock
clock_pag1.html

Clock In >> C Words
Clock In, definition of term: Clock In
clock+in_pag1.html

Clock Speed >> C Words
Clock Speed, definition of term: Clock Speed
clock+speed_pag1.html

Water Clock >> W Words
Water Clock, definition of term: Water Clock
water+clock_pag1.html

Time Clock >> T Words
Time Clock, definition of term: Time Clock
time+clock_pag1.html

Sidereal Clock >> S Words
Sidereal Clock, definition of term: Sidereal Clock
sidereal+clock_pag1.html

Pendulum Clock >> P Words
Pendulum Clock, definition of term: Pendulum Clock
pendulum+clock_pag1.html

Atomic Clock >> A Words
Atomic Clock, definition of term: Atomic Clock
atomic+clock_pag1.html