The plural form of 'Cactus' is-

• cactus
English Meaning: a plant that grows in hot dry regions, especially one with thick stems covered in spines but without leaves.
- এর তিনটি plural form হয়।
- Cacti or cactus or cactuses.

• কিছু কিছু noun এর plural অনিয়মিতভাবে হয়ে থাকে। যেমন:

Singular: Crisis - Plural: Crises
Singular: Radius - Plural: Radii
Singular: Thesis - Plural: Theses
Singular: Medium - Plural: Media

Singular: Agendum - Plural: Agenda
Singular: Datum - Plural: Data
Singular: Bacterium - Plural: Bacteria
Singular: Focus - Plural: Foci

Singular: Criterion - Plural: Criteria
Singular: Alumnus - Plural: Alumni
Singular: Fungus - Plural: Fungi

Singular: Cactus - Plural: Cacti (or Cactuses)
Singular: Octopus - Plural: Octopi (or Octopuses)
Singular: Index - Plural: Indices (or Indexes)
Singular: Appendix - Plural: Appendices (or Appendixes)

বিঃদ্রঃ 'Cacti' is the Latin plural of cactus and 'Cactuses' is the English plural.

Source:
1. A Passage to the English Language by S.M. Zakir Hussain.
2. Oxford Dictionary.