The terminology used in the parts of the Stupa

The terms Chaitya, Cetiya, Thupa, Stupa and Seya refer to the type of structure in Pali, Sanskrit and Sinhalese languages and absorbed into English, Stupa being the most commonly used. The term Dagoba is derived from Dhathughabba (relic chamber). Dagab Vahanse is a reverential term used in Sinhala generally applied to the entire structure. The circular base is built up with surrounding terraces (Medhi or Malaka, Maluwa). Concentric rings (Pesa) serve for flower offerings (Pupphadhana). The circumambulatory path (Padaksinapatha) is reached by stairways (Sopana).
Within this circle is the Dhathugabbha (relic chamber). Raised on the circular platform is the dome (Anda, Gharbha or Gharbapatra). The top of the dome has a socket (Yupi) for the parasol (Chaffa or Chatra) which is surrounded by a railing (Vedika) forming the square turret or tee (Chaturassa-caya, Harmika). The early single parasol, as mentioned to be on the Ruwanweliseya, evolved to have several tiers known as Chatravali. This later became a conical spire (Kothkaralla) or the present day pinnacle. The Chatra, the Chatravali and the pinnacle were all terminated by a metal finial (Sthupi) on which rests the crystal (now known as Chudamanikkya or Silumina).
The conical spire often rested on a cylinder. The four frontispieces although of great antiquity is said to be a later addition by King Lanji Tissa to the already constructed Mahathupa. The frontispiece is known as Ayaka or Vahalkada. The terms used here are well known and in general use, and also from many literary sources.
There are many shapes to a Stupa, Bubble-shape, Paddy-heap shape, Bell shape and so on. The building of the Mahathupa in particular, records that it was to be made in a Bubble shape (Bubulakara) of particular dimensions at the behest of the King, guided by the Theras.