The antimicrobial peptides (AMPs) are evolutionarily ancient molecules that act as components of the innate immune system. Recently, it was demonstrated that a single AMP can perform various functions; this ability is known as "peptide promiscuity." However, little is known about promiscuity in plant AMPs without disulfide bonds. This study was carried out to evaluate the promiscuity of Cn-AMP1: a promising disulfide-free plant peptide with reduced size and cationic and hydrophobic properties. Its activity against human pathogenic bacteria and fungal pathogens, as well as its in vitro immunostimulatory activity and effects on cancerous and healthy mammalian cell proliferation were studied here. Cn-AMP1 exerts antimicrobial effects against Gram-positive bacteria, Gram-negative bacteria, and fungi. Moreover, tumor cell viability activity in Caco-2 cells, as well as immunostimulatory activity by evaluating upregulated inflammatory-cytokine secretion by monocytes was also positively observed. Cn-AMP1 does not exhibit a well-defined conformation in aqueous solution and probably undergoes a 3(10)-helix transition in hydrophobic environments. The experimental results support the promiscuous activity of Cn-AMP1, presenting a wide range of activities, including antibacterial, antifungal, and immunostimulatory activity. In the future, Cn-AMP1 should be used in the development of novel biopharmaceuticals, mainly due to its reduced size and broad spectrum of activity.