awk '$1 == "word"{print}' /var/log/messages
This example assumes that word is the first field and that it consists only of "word". If the first field is "word1" this won't match.
Fixes for this are
awk '$1 ~ "word"{print}'
(this matches any occurrance of "word" in the first field)
or:
awk '/^[[:space:]]*word/ {print}'
(this matches any line starting with whitespace followed immediately by "word")