The expresssion to match rooster or hen as a complete word (i.e. not when they are part of a longer, different word):
\b(rooster|hen)\b
This is a safety measure to avoid false positives with partial matches.
The \b denotes a word boundary, which is the (zero-width) spot between a character in the range of “word characters” ([A-Za-z0-9_]) and any other character. In effect the above would:
- match in
"A chicken is either a rooster or a hen." - not match in
"Chickens are either a roosters or hens."– but(rooster|hen)would
As a side note, to allow the plural, this would do: \b(roosters?|hens?)\b