Principal English Translation: 

a large red or yellow tomato (Karttunen and Molina); an ordinary tomato (Sahagún and Chimalpahin)

Alonso de Molina: 

xitomatl. tomates grandes colorados, amarillos y blancos.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 159v. col. 1. Thanks to Joe Campbell for providing the transcription.

Frances Karttunen: 

XĪTOMA-TL pl: -MEH large red or yellow tomato ( as contrasted with the green husk tomato) / tomates grandes colorados, amarillos, y blancos (M), jitomate (T) See XĪTOM(A), TOMA-TL.
Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 326.

Attestations from sources in English: 

Auh ca nohuian quihualtocatiaque yn tlalli. auh yn quihualquitiaque. yn intech monequia. nacatl yn tonacayotl. yhua yn etl. huauhtli. chian yhuan chilli. xitomatl = And everywhere they sowed seeds in the soil, and they ate what they needed: meat and the products of the lands [like] corn, beans, amaranth, chia, chilis, and tomatoes. (central Mexico, early seventeenth century)
Codex Chimalpahin: Society and Politics in Mexico Tenochtitlan, Tlatelolco, Culhuacan, and Other Nahuatl Altepetl in Central Mexico; The Nahuatl and Spanish Annals and Accounts Collected and Recorded by don Domingo de San Antón Muñón Chimalpahin Quauhtlehuanitzin, eds. and transl. Arthur J. O. Anderson and Susan Schroeder (Norman: University of Oklahoma Press, 1997), vol. 1, 76–77.

xitomatl = ordinary tomatoes (central Mexico, sixteenth century)
Fr. Bernardino de Sahagún, Florentine Codex: General History of the Things of New Spain; Book 8 -- Kings and Lords, no. 14, Part IX, eds. and transl. Arthur J. O. Anderson and Charles E. Dibble (Santa Fe and Salt Lake City: School of American Research and the University of Utah, 1951), 68.