tathatā [tathatā] suchness. Tathatā means true nature of all things, the essence of all things. Tathatā is considered as the Ultimate Reality in the Mahāyāna mysticism. It is immanent in life, yet transcends its expression. It is beyond all concepts and distinctions, immovable and immutable.

Buddhānusmṛti - A Glossary of Buddhist Terms

Mahāyāna-Sūtrālaṅkāra. IX. 46. The Vajracchedikā. XVII. 133.Source: Buddhānusmṛti: A Glossary of Buddhist Terms

tathatā

(Sanskrit). Term meaning ‘suchness’, and denoting the way things are in truth or actuality, and used especially in Mahāyāna Buddhism to denote the essential nature of reality and the quiddity or true mode of being of phenomena which is beyond the range of conceptual thought (vikalpa). The term is one of a range of synonyms for the absolute, which include emptiness (śūnyatā), thusness (tattva), the limit of reality (bhūta-koṭi), and true suchness (bhūta-tathatā).

A Dictionary of Buddhism, Oxford University Press, 2003, 2004 (which is available in electronic version from answer.com)

tathatā : [f.] reality; such likeness.

A.P. Buddhadatta Mahathera, Concise Pali-English and English-Pali Dictionary [available as digital version from Metta Net, Sri Lanka]

Tathatā (f.) [abstr. fr. tathā>tatha] state of being such, such -- likeness, similarity, correspondence Vism 518.

Pali-English Dictionary, TW Rhys Davids, William Stede,

de kho na nyid

[translation-san] {MSA} tattva

[translation-san] {MSA} satya

[translation-san] tathatā

[translation-eng] {Hopkins} [that-only-ness]; reality; suchness [i.e., emptiness]

Jeffrey Hopkins' Tibetan-Sanskrit-English Dictionary

de nyid

[tenses]

• de
• kho
• na
• nyid

[translation-san] {C,MSA} tattva

[translation-san] {MSA} satattva

[translation-san] tathatā

[translation-eng] {Hopkins} reality; suchness; principle

[translation-eng] {C} just that; Thatness; truly real; 'thatness'; reality itself

Jeffrey Hopkins' Tibetan-Sanskrit-English Dictionary

de bzhin nyid

[translation-san] {LCh,MV,MSA} tathatā

[translation-san] {C,MSA} tathātva

[translation-san] {MV} tathātā

[translation-san] {MSA} tattva

[translation-eng] {Hopkins} suchness; thusness

[comments] Comment: An equivalent of ultimate truth (don dam bden pa, paramārthasatya) so called because whether Buddhas arise or not it permanently abides thus without changing.

Jeffrey Hopkins' Tibetan-Sanskrit-English Dictionary