1) an accident, especially one involving loss of life or seriously injury (casualty)

2) wanting something seriously (desirous)

3) to (fix one's attention on something and) think seriously and deeply (about it) (meditate)

4) seriously thoughtful (pensive)

5) to use bad, obscene, language; to state or promise (something) seriously and formally (swear)

6) something, e.g. a doll, used for a child to play with; (of a dog) very small; to think not very seriously about a possibility etc (toy)