The best replacement for cosine is sine.

The best alternatives to cosine are rated as following:
★★★★★  sine
★★  secant
★  sine wave
★  sine graph
★  sine graphs
★  sin
  jaccard
  sine curve
  sine signal

Your alternative for cosine is not listed? Suggest!
Speaking about cosine, one probably shouldn't forget about phase shift.

Other search terms related to cosine and their ratings are:
★★★★★ phase shift
You have in mind a companion for cosine and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of cosine in all years. Click on graph for more.
cosine
sine
secant