In Sikh Religion, Siva is power of Almighty. It is synonym to like Hukam(command), Shakti(power), Vivek Budhi(Intuitive/discerning mind), Gyan Khadag(The sword of wisdom/Gurmat) and most important expression in dictionary of Sikhs. In Dasam Granth, the expression Sada Siv is used for Nirankar(Formless Lord) but not for diety of hinduism called Mahadeva. Sly, in Guru Granth Sahib Siv is used primarily for Karta. This term is popularly used in following Shabad:
ਨ ਡਰੋਂ ਅਰਿ ਸੋ ਜਬ ਜਾਇ ਲਰੋਂ ਨਿਸਚੈ ਕਰਿ ਅਪੁਨੀ ਜੀਤ ਕਰੋਂ ॥
ਅਰੁ ਸਿਖ ਹੋਂ ਆਪਨੇ ਹੀ ਮਨ ਕੌ ਇਹ ਲਾਲਚ ਹਉ ਗੁਨ ਤਉ ਉਚਰੋਂ ॥
In Parallel, Hinduism use this term for Parvati, who was wife of Mahadeva. Including this other expression like Shakti, Durga, Chandika, Kalika etc. is used for physical body i.e Parvati which is not in case of Sikh Religion.
Guru Granth Sahib contains many religious terminologies from past religions, whose real spiritual meanings were explained by Gurus and Bhagats. For example: From Vaishnavites, the expressions Damodar, Beethula, Jagannath, Hari, Gobind, Murari, Rama, Sia, etc.; from Nath tradition Mundra, Jholi, Biphuti etc; from Islam Mecca(Mann), Kibla(Dehi) etc.; from Buddhism buddha, nirvana etc.;From Guru Tradition, Gur, Guru, Satgur, Sikha etc. In Dasam Granth, expressions from Shaivism and Shaktism are sanctified enormously.
Where Sada Siv is qualitative aspect of almighty, Sly, Siva is aspect of Shakti(or Hukam in Masculine form) of Almighty.
Sikh point of view
In Gurmat Interpretations,
- ਸਿਵ, ਸਕਤਿ ਆਪਿ ਉਪਾਇ ਕੈ, ਕਰਤਾ ਆਪੇ ਹੁਕਮੁ ਵਰਤਾਏ ॥ : Siv(Karta) has manifested Shakti(Hukam) i.e from Sunn Samadhi to Sehaj Samadhi.
Guru Gobind Singh gave that Sakti of Siv = Shiva. He said ਦੇਹ ਸਿਵਾ ਬਰ ਮੋਹਿ ਇਹੈ ਸਭ ਕਰਮਨ ਤੇ ਕਬਹੂੰ ਨ ਟਰੋਂ ॥. Gobind Singh as a devotee is asking Siva = Hukam = Shakti of God to help him so that he may not hesitate from performing good actions.