import re
p = re.compile(ur'\b(yest(?:e(?:r(?:d(?:ay?)?)?)?)?|tod(?:ay?)?|tom(?:o(?:r(?:r(?:ow?)?)?)?)?)\b', re.IGNORECASE)
test_str = u"yest\nyeste\nyester\nyesterd\nyesterda\nyesterday\ntod\ntoda\ntoday\ntom\ntomo\ntomor\ntomorr\ntomorro\ntomorrow\n\nyesteray\ntomorow\ntommorrow\ntody\nyesteday"
print(p.findall(test_str))