Tom

Tom is a short form of the forename Thomas. There are two main types of such shortenings: they are convenient for writing, e.g. in lists; or they are essentially spoken pet-names, and thus informal. (See Conventional abbreviations for forenames.)

Short form	Long form	Informal or written	Other short forms	Remarks
Tom	Thomas	Informal	Tam; Tammy; Tommy

There is a list of similar names at Conventional abbreviations for forenames, as well as the category:short names

Note that any informal form may be spelled in different ways. Notably, any spelling listed that ends in '-ie' may be written with the ending '-y', and vice versa.

• Tom has been close to a stereotypical name for 'an ordinary Englishman'. This was particularly exploited in the eponymous heroes of two novels, Tom Jones (1749) and Tom Brown's Schooldays (1857), although it is even clearer in the use of Tommy for the archetypical British soldier. This status may have influnced the choice of 'Tom' by various writers, including 'Mark Twain', in his novel Tom Sawyer and Harriet Beecher Stowe in Uncle Tom's Cabin
• The phrase "[every] Tom Dick and Harry" means 'ordinary people', a hypothetical random sample; or a dismissive term for 'the ordinary people [not like us]'.
• Tom Thumb is a diminutive character in folklore. He is 'no bigger than his father's thumb'. The name has become a byword for small persons, including 'General' Tom Thumb, the stage name of a ninteenth century dwarf made famous by the Barnum circus organization.
• A tom, as a common noun, is short for tomcat i.e. a male cat. The verb 'to tomcat around' is said of a male. It is not polite: it means 'to behave with indiscriminate sexual promiscuity', 'to prey on many women'- to behave as male cats are seen to do.

(The name is after the forename: OED traces it thus: "In 1760 was published an anonymous work The Life and Adventures of a Cat, which became very popular. The hero, a male or ‘ram’ cat, bore the name of Tom, and is commonly mentioned as ‘Tom the Cat’, as ‘Tybert the Catte’ is in Caxton's Reynard the Fox. Thus Tom became a favourite allusive name for a male cat ... and people said 'this cat is a Tom' or a 'Tom cat'.")

• The 7-ton bell at Christ Church College in Oxford is known as Great Tom. It is housed in Tom Tower in Tom Quad, and is rung 101 times every night, originally a a curfew signal.