thūpa : [m.] a tope; pagoda; a cairn; a monument erected over the ashes of a holy person.

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

Thūpa [Vedic stūpa, crown of the head, top, gable; cp. Gr. stu/pos (handle, stalk). Oicel. stūfr (stump), to *steud as in tudati] a stupa or tope, a bell -- shaped pile of earth, a mound, tumulus, cairn; dome, esp. a monument erected over the ashes of an Arahant (otherwise called dhātugabbha=dāgaba), or on spots consecrated as scenes of his acts. In general as tomb: Vin iv.308; J iii.156 (mattika˚)=Pv i.84; in special as tope: D ii.142, 161, 164 sq.; A i.77; M ii.244; J v.39 (rajata˚); VvA 156 (Kassapassa bhagavato dvādasayojanikaŋ kanaka˚); Ud 8; Pv iii.105. Four people are thūpârahā, worthy of a tope, viz. a Tathāgata, a Tathāgatasāvaka, a Paccekabuddha, a Cakkavattin D ii.143= A ii.245. -- At Dpvs vi.65 th. is to be corrected into dhūpaŋ.

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

stūpa [thūpa] relic, shrine. A stūpa is a Buddhist monument where the relics of Śākyamuni or other saints are preserved. The stūpa-s are of a particular shape. Generally they are dome-shaped or mound shaped. In East Asia they are in the form of tower like pagodas. When the monument is erected over the relic of the Buddha such as bones, hair or teeth, it is known as dhātustūpa.

     King Ajātaśatru proposed to build a stūpa over the relic of the Buddha and so did the Licchavis and others. The claimants built eight stūpa-s in their respective territories. Two stūpa-s were erected over the vessel used in cremation and the ashes. Thus in Buddhism the cult of stūpa-s came into existence.

Dīgha Nikāya. Mahāparinibbāna. Khuddaka Nikāya. Upavāṇattherapadānam. Saddharmapuṇḍarīkasūtram. I. 18; II. 68, 306-316. Śrī Guhyasamāja Tantra or Tathāgataguhyaka. VIII. 26.

Buddhānusmṛti - A Glossary of Buddhist Terms

A religious monument which evolved from the prehistoric tumulus or burial mound into a dome-shaped structure such as the early Indian stūpas at Sāñcī. To this shape a spire was subsequently added, and the final phase of development was the pagoda style of tower found throughout east Asia. Stūpas were built originally to commemorate a Buddha or other enlightened person, a practice validated by the Buddha in theMahāparinibbāna Sutta where he leaves instructions that a stūpa is to be constructed over his relics. As well as relics, stūpas often contain sacred objects, such as texts. A small replica of a stūpa is often used as a reliquary.

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